Introduction
Logical reasoning is a fundamental skill tested in various competitive exams, aptitude tests, and assessments. One of the key components of logical reasoning is the Letter Series, where candidates must identify patterns in sequences of letters and predict the next element(s) in the series.
This lecture will cover:
- Understanding Letter Series
- Common Types of Letter Series Patterns
- Strategies to Solve Letter Series Questions
- Practice Examples
1. Understanding Letter Series
A letter series is a sequence of letters that follows a specific logical rule. The task is to identify the underlying pattern and determine the missing or next letter(s) in the series.
Why is it Important?
- Enhances pattern recognition skills.
- Improves analytical and logical thinking.
- Frequently tested in exams like CAT, GRE, GMAT, Bank PO, SSC, and other aptitude tests.
2. Common Types of Letter Series Patterns
(A) Alphabetical Order-Based Series
The series follows the natural order of the English alphabet (A, B, C, D, … Z).
Examples:
- A, C, E, G, ?
- Pattern: +2 letters (A → C → E → G → I)
- Answer: I
- Z, X, V, T, ?
- Pattern: -2 letters (Z → X → V → T → R)
- Answer: R
(B) Position-Based Series
Letters are related to their numerical position in the alphabet (A=1, B=2, …, Z=26).
Examples:
- D, G, J, M, ?
- Positions: 4 (D), 7 (G), 10 (J), 13 (M), ?
- Pattern: +3
- Next: 16 → P
- A, D, I, P, ?
- Positions: 1 (A), 4 (D), 9 (I), 16 (P), ?
- Pattern: Squares of natural numbers (1², 2², 3², 4², 5² → 25 = Y)
- Answer: Y
(C) Letter Repetition & Skipping
Letters repeat or skip in a particular order.
Examples:
- A, A, B, C, C, D, E, E, ?
- Pattern: Repeat every alternate letter (A,A / B / C,C / D / E,E / F)
- Answer: F
- A, C, B, D, C, E, D, ?
- Pattern: Alternate +2 and -1 (A→C→B→D→C→E→D→F)
- Answer: F
(D) Reverse Alphabet Series
The series moves backward in the alphabet.
Example:
- D, W, G, T, J, Q, ?
- Pattern: Alternate +3 (D→G→J→M) and -3 (W→T→Q→N)
- Next: M
(E) Mixed Letter Patterns
Combination of different rules (e.g., vowels, consonants, word-based patterns).
Examples:
- A, E, B, F, C, G, ?
- Pattern: Alternate vowels (A,E) and consonants (B,F,C,G,D)
- Answer: D
- AB, BC, CD, DE, ?
- Pattern: Consecutive letter pairs (AB → BC → CD → DE → EF)
- Answer: EF
3. Strategies to Solve Letter Series Questions
- Observe the Series Carefully – Look for immediate jumps (+2, -3, etc.).
- Check Alphabet Positions – Convert letters to numbers if needed.
- Look for Alternate Patterns – Sometimes two different rules alternate.
- Check Reverse Alphabet – Some series move backward (Z, Y, X…).
- Practice Common Patterns – Familiarity helps in quick recognition.
4. Practice Examples
Exercise: Find the next letter in the series.
- B, E, H, K, ?
- A, Z, B, Y, C, ?
- C, F, I, L, ?
- M, N, O, M, N, O, P, ?
- AB, DE, GH, JK, ?
Answers:
- N (+3 pattern)
- X (Alternate forward A,B,C and backward Z,Y,X)
- O (+3 pattern)
- M (MNO repeated with an extra P, then restart)
- MN (Pairs with +3 gap: AB → DE → GH → JK → MN)
Practice Test
30 MCQs on Letter and word Series
1. A, C, E, G, ?
a) H
b) I
c) J
d) K
Answer: (b) I
Explanation: The series follows +2 letters (A → C → E → G → I).
2. B, D, G, K, ?
a) N
b) O
c) P
d) Q
Answer: (c) P
Explanation: The pattern is +2, +3, +4, +5 (B→D→G→K→P).
3. Z, X, V, T, ?
a) R
b) S
c) Q
d) P
Answer: (a) R
Explanation: The series moves backward with -2 letters (Z → X → V → T → R).
4. A, D, I, P, ?
a) U
b) W
c) Y
d) Z
Answer: (c) Y
Explanation: The letters correspond to square numbers (1²=A, 2²=D, 3²=I, 4²=P, 5²=Y).
5. C, F, I, L, ?
a) M
b) N
c) O
d) P
Answer: (c) O
Explanation: The pattern is +3 letters (C → F → I → L → O).
6. AB, BC, CD, DE, ?
a) EF
b) FG
c) GH
d) HI
Answer: (a) EF
Explanation: Consecutive letter pairs (AB → BC → CD → DE → EF).
7. A, B, D, G, K, ?
a) O
b) P
c) Q
d) R
Answer: (b) P
Explanation: The pattern is +1, +2, +3, +4, +5 (A→B→D→G→K→P).
8. D, W, G, T, J, Q, ?
a) M
b) N
c) O
d) P
Answer: (a) M
Explanation: Alternate +3 (D→G→J→M) and -3 (W→T→Q→N).
9. A, Z, B, Y, C, ?
a) W
b) X
c) D
d) V
Answer: (b) X
Explanation: Alternate forward (A,B,C) and backward (Z,Y,X).
10. M, N, O, M, N, O, P, ?
a) M
b) N
c) O
d) Q
Answer: (a) M
Explanation: The series repeats MNO and adds P, then restarts.
11. B, E, H, K, ?
a) L
b) M
c) N
d) O
Answer: (c) N
Explanation: The pattern is +3 letters (B → E → H → K → N).
12. A, C, F, J, ?
a) M
b) N
c) O
d) P
Answer: (c) O
Explanation: The pattern is +2, +3, +4, +5 (A→C→F→J→O).
13. P, O, N, M, ?
a) L
b) K
c) J
d) I
Answer: (a) L
Explanation: The series moves backward (-1 letter each time).
14. AZ, BY, CX, DW, ?
a) EV
b) FU
c) GV
d) HU
Answer: (a) EV
Explanation: First letter moves forward (A,B,C,D,E), second letter moves backward (Z,Y,X,W,V).
15. A, E, B, F, C, G, ?
a) D
b) E
c) H
d) I
Answer: (a) D
Explanation: Alternate vowels (A,E) and consonants (B,F,C,G,D).
16. D, H, L, P, ?
a) R
b) S
c) T
d) U
Answer: (c) T
Explanation: The pattern is +4 letters (D → H → L → P → T).
17. AB, DE, GH, JK, ?
a) LM
b) MN
c) NO
d) OP
Answer: (b) MN
Explanation: Each pair skips 2 letters (AB → DE → GH → JK → MN).
18. A, C, B, D, C, E, D, ?
a) E
b) F
c) G
d) H
Answer: (b) F
Explanation: Alternate +2 (A→C→B→D→C→E→D→F) and -1.
19. X, U, R, O, ?
a) L
b) M
c) N
d) K
Answer: (a) L
Explanation: The pattern is -3 letters (X → U → R → O → L).
20. B, C, E, H, L, ?
a) O
b) P
c) Q
d) R
Answer: (c) Q
Explanation: The pattern is +1, +2, +3, +4, +5 (B→C→E→H→L→Q).
21. A, Z, C, X, E, ?
a) V
b) W
c) U
d) T
Answer: (a) V
Explanation: Alternate forward (A,C,E) and backward (Z,X,V).
22. J, L, O, S, ?
a) V
b) W
c) X
d) Y
Answer: (c) X
Explanation: The pattern is +2, +3, +4, +5 (J→L→O→S→X).
23. E, J, O, T, ?
a) W
b) X
c) Y
d) Z
Answer: (c) Y
Explanation: The pattern is +5 letters (E → J → O → T → Y).
24. C, G, K, O, ?
a) Q
b) R
c) S
d) T
Answer: (c) S
Explanation: The pattern is +4 letters (C → G → K → O → S).
25. A, B, D, G, K, ?
a) P
b) Q
c) R
d) S
Answer: (a) P
Explanation: The pattern is +1, +2, +3, +4, +5 (A→B→D→G→K→P).
26. BD, EG, HJ, KM, ?
a) NP
b) OQ
c) PR
d) QS
Answer: (a) NP
Explanation: Each letter in the pair moves +2 steps (B→D, E→G, H→J, K→M, N→P).
27. A, D, I, P, ?
a) U
b) V
c) W
d) Y
Answer: (d) Y
Explanation: The letters correspond to square numbers (1²=A, 2²=D, 3²=I, 4²=P, 5²=Y).
28. Z, Y, X, W, ?
a) V
b) U
c) T
d) S
Answer: (a) V
Explanation: The series moves backward (-1 letter each time).
29. AB, BC, CD, DE, ?
a) EF
b) FG
c) GH
d) HI
Answer: (a) EF
Explanation: Consecutive letter pairs (AB → BC → CD → DE → EF).
30. A, C, E, G, ?
a) H
b) I
c) J
d) K
Answer: (b) I
Explanation: The pattern is +2 letters (A → C → E → G → I).
